This invention relates to photovoltaic materials, and, more particularly, to such materials which are active over a wide range of the electromagnetic spectrum.
Photovoltaic materials respond to particular regions of the electromagnetic spectrum to produce an electrical output. Thus amorphous silicon reacts to visible light in the range up to about 6,000 to 7,000 Angstroms. Similarly crystalline silicon is responsive to electromagnetic energy in the range up to about 1.1 to 1.2 microns. Other semiconductors are active in still other regions of the electromagnetic spectrum.
As a result no single semiconductor material is able to make use of the entire spectrum to which it is typically exposed. In addition the conversion efficiency of the spectral energy depends upon the particular semiconductor. Typical values for amorphous silicon range upwardly from about 41/2%. Similarly typical values for crystalline silicon range upwardly from about 6%. It is apparent that in the case of amorphous silicon approximately 95 percent of the excitation energy is unconverted. Likewise, in the case of crystalline silicon, approximately 94 percent of the excitation energy is unconverted.
Although crystalline silicon presently has a greater conversion efficiency than its amorphous counterpart, it is costly to produce and difficult to employ with other semiconductor materials. In particular, crystalline silicon requires a minimum thickness for proper handling that prevents it from being successfully employed with other materials. Thus there is a significant fragility which often leads to breakage and crackage during even the routine handling of amorphous silicon.
Accordingly, it is an object of the invention to make better use of the electromagnetic spectrum in the excitation of semiconductor materials. A related object is to increase the extent to which the excitation spectrum is converted into electricity by semiconductor materials. Another related object is to increase the overall conversion efficiency for electromagnetic energy.
Another object of the invention is to facilitate the employment of crystalline semiconductors. A related object is to facilitate the employment of such semiconductors in combination with other materials. A related object is to reduce the extent of breakage and crackage that is presently encountered in the manipulation of crystalline materials, particularly crystalline semiconductors.